1. Field of the Invention
The present invention relates to the field of luminaires, and more specifically relates to the field of luminaires employing means to provide even, glare-free illumination.
2. Description of the Prior Art
The problem of reducing the harshness of lighting emanating from lighting fixtures is one with which the art has been struggling for many years. Early solutions included diffusers, i.e. translucent sheets placed between the light source and the area external to the lighting fixture in order to reduce glare and to provide more even, softer lighting. Examples of such devices are the commonly-seen frosted glass portions of light fixtures. Also, Wilson, in U.S. Pat. No. 3,460,299 which issued on Aug. 12, 1969, proposed a ceiling made up of opalescent plastic panels with a double thickness to provide both illumination and sound deadening.
A solution widely adopted by the art has been to provide a cellular structure beneath the light source to diffuse the illumination. As originally proposed, such structures featured a simple gridwork, also referred to as the "egg crate" design, as seen in U.S. Pat. No. 2,607,455 which issued on Aug. 19, 1952.
Adaptations of such structures provided the gridwork in a curved form, as in U.S. Pat. No. 2,837,632 which issued on June 3, 1958 to Lipscomb. A later development was the introduction of curved sides for the gridwork members as in U.S. Pat. Nos. 4,272,804 which issued on June 9, 1981 to Blum and 2,971,083 which issued on Feb. 7, 1961 to Phillips. Such curved sides result in multiple reflection of light rays directed away from the vertical which provides even illumination below the luminaire.
Generally, the gridwork is provided with both the top and bottom surfaces open in order to give the maximum transmission of light; however, some constructions provide for a diffuser surface simply above the grid work. For example, Jones, in U.S. Pat. No. 3,996,458 which issued on Dec. 7, 1976, Cutler, in U.S. Pat. No. 3,152,277 which issued on Oct. 6, 1964 and Schwartz, U.S. Pat. No. 3,922,073 which issued on Nov. 25, 1975, disclose various embodiments of a cellular diffusing structure which is combined with a planar diffuser closing the upper ends of the cells. Although many permutations and combinations of these ideas have been proposed including various shapes for the cells and various materials for the structure, the art has found no utility to be gained through closing the lower ends of the cells.
The increased use of microcomputers in the business environment has led to an increased awareness of the advantages of cellular luminaire design. It has been found that the lighting pattern produced by conventional, non-cellular illumination fixtures presents a significant reflected glare problem on the screen of the cathode ray tube of a computer terminal or a word processor. Although some installations employ "filter" screens of dark-colored, fine mesh to reduce reflected glare from the screen, such "filters" substantially reduce the light level of the images on the screen. Another approach has been to install cellular luminaires. Not only is improvement seen in general lighting through this approach, but also glare is significantly reduced, concomitantly reducing worker fatigue, headaches, and eye strain. The most efficient cellular structures for reducing such glare have been found to employ relatively small cell sizes, for example, in the range of 1/4 inch to 11/2 inches.
A serious problem that has not been addressed by the art, however, is that of maintaining cellular luminaire structures after installation. In the typical open-ended construction, large volumes of air flow through the luminaire, driven by the convection currents set up by the heat of the lighting elements such as fluorescent lamps. Even when the upper ends of the cellular structure is closed off by a diffuser sheet overlying the cellular structure, the heating of the cellular structure by the lamps causes appreciable air flows around the bottom surface and the cells. As a result, dust becomes steadily accumulated on the surfaces of the cellular structure. Over a relatively short period of time, the dust build-up appreciably degrades the ability of the cell walls to reflect light, reducing the overall illumination provided by the fixture. In addition, the accumulation of dust is unsightly. In order to remove such build up, a significant maintenance effort is required to clean the cell walls. The magnitude of this effort can be appreciated by considering the work involved in cleaning a luminaire measuring 2.times.4 feet, which, assuming a widely-used cell size of 1 inch by 1 inch, involves the cleaning of 1,152 sets of cell walls. Moreover, the small size of such cells exacerbates the problem, requiring laborious hand work to remove dust and grime. Typically such cleaning operations require large tubs or vats in which the cellular structure is submerged for washing and rinsing. Thereafter, the cellular structures must be dried, polished, etc. To date, the prior art offers no solution to this problem, No devices, whether on the market or discussed in U.S. patents or other references, combine the lighting advantages of the cellular luminaire with ease of maintenance.